fix(tts): support integrated GPU backends in MagpieTTS and NanoCodec

[hsuanguo]

Got this error:

--lt-backend cuda requires a CUDA ggml backend; current backend is CPU
nemo-speech serve: MagpieTTS synthesis failed

Add an IGPU initialization attempt after discrete-GPU initialization fails, before the existing CPU fallback, in both MagpieTTS and NanoCodec.

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📥 Commits

Reviewing files that changed from the base of the PR and between b809bbb and 864559c.

📒 Files selected for processing (2)

• src/tts/magpietts/model.cpp
• src/tts/nanocodec/model.cpp

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📝 Summary

Summary by CodeRabbit

• Improvements
  • MagpieTTS and NanoCodec now try an integrated GPU when the primary GPU is unavailable, before falling back to CPU.
  • When CPU is forced, GPU initialization is skipped.

Walkthrough

MagpieTTS and NanoCodec now attempt integrated-GPU initialization after GPU initialization fails. The existing CPU fallback remains. The integrated-GPU attempt is skipped when CPU is forced.

Changes

TTS backend fallback

Layer / File(s)	Summary
Integrated GPU fallback src/tts/magpietts/model.cpp, src/tts/nanocodec/model.cpp	When CPU is not forced and GPU initialization fails, both model loaders try the integrated GPU backend before the existing CPU fallback.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 86455

The change adds an integrated-GPU attempt before the existing CPU fallback. No actionable merge-blocking risk is established by the available evidence.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the integrated-GPU backend support added for MagpieTTS and NanoCodec.
Description check	✅ Passed	The description explains the reported backend error and the integrated-GPU initialization attempt added before the CPU fallback in both models.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[greptile-apps]

Confidence Score: 4/5

[Medium risk] Adds integrated GPU fallback to text-to-speech model loading.

The PR should not merge until an IGPU allocation failure can fall back to CPU without aborting synthesizer creation.

Findings

1.  IGPU allocation prevents CPU fallback ▶

Summary

The PR adds integrated-GPU initialization between discrete-GPU initialization and CPU fallback for MagpieTTS and NanoCodec.

• Model allocation failure after IGPU initialization does not fall back to CPU.

_{Reviews (1) · Last reviewed commit: "fixed tts loaders on igpu"}

[greptile-apps]

IGPU allocation prevents CPU fallback

If an integrated GPU initializes but lacks enough memory for the model tensors, loading returns an error instead of trying the CPU backend. NanoCodec has the same path. Either failure stops synthesizer creation, even though the CPU fallback could have loaded the model. Retry loading on CPU when IGPU allocation fails, or check capacity before selecting the IGPU.

[anand-nv]

Can I know what is the hw platform you are trying to deploy this on?

[hsuanguo]

Can I know what is the hw platform you are trying to deploy this on?

Hi, it's Jetson Orin on Jetpack 7.2